IBM SG24-6320-00 manual Caching, Dynacache

Draft Document for Review July 28, 2004 7:33 pm 6320ch_sum_of_changes.fm

2.6.15 Caching

Server-side caching improves response time and reduces system load thus boosting performance and reducing infrastructure costs. The WebSphere Commerce servlet and page caching is now part of the WebSphere Application Server dynamic caching infrastructure (Dynacache).

Dynacache

WebSphere Application Server offers a built-in dynamic cache service for serving dynamic content and caching data. There is no time-consuming installation and integration work needed to activate. DynaCache can be viewed as a sophisticated hash table, where Java object store and retrieve commands are executed in memory.

Some of the features of WebSphere Application Server dynamic cache (DynaCache) are servlet/JSP result cache, replication support, invalidation support, Edge of Network caching support and tools to assist in configuring the cache and monitoring runtime.

The cache policy is defined by a policy based cachespec.xml file. Some of the cacheable objects defined by this policy include: servlet/JSP files, command beans, Web services, cache and dependency ID's generation rules, replication policy, invalidation rules, time-out, and priority for least recently used eviction algorithm. The cachespec.xml file resides inside the Web Module WEB-INF directory and a copy of this file can be placed in the application server properties directory. It is also flexible and modifiable at runtime.

This type of cache also supports fragment caching. This is the ability to cache portions of a page. For example, instead of caching a full page MyJSP.jsp, you can choose to cache fragments, which can include the header, footer, sidebar and the main area. All of these fragments are dynamic pages that are part of the larger dynamic page for MyJSP.jsp. There is a performance gain in fragment caching but it is not dramatic because the non-cached parts of the page determine the performance.

Replication support enables cache sharing (central cache) and replication (local cache) among multiple servers and tiers. Replication uses a built-in high performance JMS broker messaging system as its underlying engine for data replication. In local cache replication among server, if there is a update to the cache, the cache server publishes a message regarding the change to the messaging broker and the changes are automatically replicated to the other servers.

Some factors to consider for fragment caching include reusability, invalidation and variations. Fragments should be able to be reused frequently enough by

Chapter 2. WebSphere Commerce V5.6 Overview 33